The invention relates to a method for controlling an internal combustion engine. The invention also relates to a computer program, a computer readable medium, a control unit, an internal combustion engine, and a vehicle.
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment, such as wheel loaders, haulers and excavators. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as buses, construction equipment and passenger cars. The invention may also be used on other transportation means such as ships and boats.
For a vehicle internal combustion engine, such as a diesel type engine for a heavy-duty vehicle, an exhaust after treatment system (EATS) is usually provided to reduce emissions, e.g. of nitrogen oxides (NOx). Such a system, which may include units such as a selective catalytic reduction (SCR) converter, requires exhaust gas temperatures that are relatively high in order to provide an efficient emission reduction.
However, measures to reduce fuel consumption may reduce the heat loss from the engine to the EATS. Therefore, particularly at low load operation, cold ambient temperatures, and/or cold start events, the EATS might not get enough heat to operate efficiently.
US2015040560A1 discloses, for increasing the temperature in an EATS when cold starting an engine, an exhaust gas recirculation (EGR) pipe which is branched off at an exhaust gas manifold part assigned to an inactive cylinder group. The EGR pipe forces air to an intake manifold part assigned to an active cylinder group. Each cylinder group comprises an intake throttle, which is adapted to be separably operable. The air intake upstream of the active intake manifold is throttled to increase the forced air flow. Although this may provide some improvement in cold start situations, there is still a need to further increase EATS temperatures at low load operations.
It is desirable to reduce emissions from internal combustion engines. It is also desirable to improve the after treatment of exhaust gases from internal combustion engines at low load operations.
According to an aspect of the invention, a method is provided for controlling an internal combustion engine comprising at least one first cylinder and at least one second cylinder with respective reciprocating pistons, each of the first and second cylinders being arranged to receive air from a fresh air intake arrangement, to receive fuel, and to provide repetitive combustions by means of the received air and fuel, the method comprising
receiving in the first cylinder air from the fresh air intake arrangement,
expelling from the first cylinder gases in the form of the air received in the first cylinder or gases including at least a portion of the air received in the first cylinder,
guiding to the second cylinder gases expelled from the first cylinder,
injecting fuel into the second cylinder so as to provide repetitive combustions with air in the gases guided from the first cylinder to the second cylinder,
and, while guiding to the second cylinder gases expelled from the first cylinder, throttling or inhibiting the supply to the second cylinder of air from the fresh air intake arrangement,
wherein guiding to the second cylinder gases expelled from the first cylinder comprises guiding to the second cylinder all gases expelled from the first cylinder.
Receiving in the first cylinder air from the fresh air intake arrangement and guiding to the second cylinder gases expelled from the first cylinder provides for heating by pre-conditioning of the air. Throttling or inhibiting the supply to the second cylinder of air from the fresh air intake arrangement limits temperature reductions caused by introduction of fresh air.
In addition, guiding to the second cylinder all gases expelled from the first cylinder means that no gases introduced to the first cylinder will reach an exhaust after treatment system (EATS) arranged to receive exhaust gases from the engine, without passing the second cylinder. Thereby the mass flow through the engine may be substantially decreased, and a further significant increase of the temperature of gases reaching the EATS at low load operations, cold start events or low ambient temperatures may be provided. This will improve the after treatment of exhaust gases from the engine, e.g. at low load, and thereby engine emissions will be reduced.
Also, the second cylinder combustions per se may be controlled without consideration for keeping exhaust gas temperatures high. Therefore the emission reduction may be provided without having to compromise running the engine for an optimal fuel efficiency.
The invention may significantly improve exhaust after treatment processes of diesel engines at extended low load or idling operations, such as operations of asphalt laying vehicles, in queues or in city driving.
Preferably, expelling gases from the first cylinder comprises expelling from the first cylinder the same amount of air as received in the first cylinder. Thereby, fuel injection into the first cylinder may be terminated so as to avoid combustions therein. Nevertheless, the air may be heated by compression in the first cylinder. The method may comprise injecting fuel into the first cylinder so as to provide repetitive combustions with the air received in the first cylinder. Thereby, heating of the gases reaching the second cylinder may be increased by the combustion in the first cylinder, whereby the overall heating capacity of the process is increased.
The method may advantageously comprise switching between a first mode with no injection of fuel into the first cylinder, and a second mode with injection of fuel into the first cylinder so as to provide repetitive combustions with the air received in the first cylinder. It should be noted that preferably the amount of fuel injected into the first cylinder is smaller, preferably considerably smaller, than the amount of fuel injected into the second cylinder.
According to another aspect of the invention, a method is provided for controlling an internal combustion engine comprising at least one first cylinder and at least one second cylinder with respective reciprocating pistons, each of the first and second cylinders being arranged to receive air from a fresh air intake arrangement, to receive fuel, and to provide repetitive combustions by means of the received air and fuel, the method comprising
receiving in the first cylinder air from the fresh air intake arrangement,
expelling from the first cylinder gases in the form of the air received in the first cylinder or gases including at least a portion of the air received in the first cylinder,
guiding to the second cylinder gases expelled from the first cylinder,
injecting fuel into the second cylinder so as to provide repetitive combustions with air in the gases guided from the first cylinder to the second cylinder,
and, while guiding to the second cylinder gases expelled from the first cylinder, throttling or inhibiting the supply to the second cylinder of air from the fresh air intake arrangement,
the method further comprising injecting fuel into the first cylinder so as to provide repetitive combustions with the air received in the first cylinder.
As also suggested above, injecting fuel into the first cylinder so as to provide repetitive combustions with the air received in the first cylinder may advantageously increase heating of the gases reaching the second cylinder, whereby the overall heating capacity of the process is increased.
Preferably, where each of the first and second cylinders is arranged to receive air from the fresh air intake arrangement via first and second intake guides, respectively, expelling gases from the first cylinder is done by means of an exhaust guide extending from the first cylinder, e.g. to the atmosphere via an EATS, and guiding to the second cylinder gases expelled from the first cylinder comprises at least partly closing an exhaust valve in the exhaust guide. For example, guiding to the second cylinder gases expelled from the first cylinder may be done by means of a recirculation guide extending from the exhaust guide and to the second intake guide, and the exhaust valve may be provided downstream of the recirculation guide. The exhaust valve may effectively provide for selectively guiding a portion or all of the gases from the first cylinder into the recirculation guide.
Said exhaust guide may be referred to as a first exhaust guide. The expelling gases from the second cylinder may be done by means of a second exhaust guide extending from the second cylinder. Preferably, the first and second exhaust guides merge downstream of the exhaust valve.
Preferably a turbine of a turbo charger is located downstream of the exhaust valve. Thereby, such a location of the exhaust valve may secure that heat is not lost by expansion in the turbine before the gases reach the second cylinder. The exhaust valve may prevent a partial flow to the turbine, and secure that all gases expelled from the first cylinder are guiding to the second cylinder.
Preferably, where each of the first and second cylinders is arranged to receive air from the fresh air intake arrangement via first and second intake guides, respectively, at least one compressor is provided upstream of the first and second intake guides and downstream of the fresh air intake arrangement. Thereby, an advantageous arranged of a single compressor service the two intake guide may be provided.
Preferably, where each of the first and second cylinders is arranged to receive air from the fresh air intake arrangement via first and second intake guides, respectively, the expelling of gases from the first cylinder is done by means of a first exhaust guide extending from the first cylinder, and guiding to the second cylinder gases expelled from the first cylinder is done by means of a recirculation guide extending from the first exhaust guide and to the second intake guide, the method further comprises expelling from the second cylinder gases by means of a second exhaust guide extending from the second cylinder, e.g. to the atmosphere via an EATS, and recirculating gases from the first and second exhaust guides to the first and second cylinder by means of an exhaust gas recirculating (EGR) passage provided in addition to the recirculation guide.
Thus the recirculation guide may be provided in addition to the EGR passage. The recirculation guide may bypass the EGR passage. Thereby, the EGR passage may be used in a traditional manner, at most operational situations, and include an EGR cooler for reducing the temperature of recirculated exhaust gases. By the recirculation guide, the heating process described above, e.g. for low load operation, may be provided without interference or adverse effect of the EGR cooler. A valve may be provided to control and selectively inhibit gas flow through the EGR passage. It should be noted however, that the method may involve guiding gases through the EGR passage as well as through the recirculation guide.
The method may comprise compressing in the second cylinder the gases guided to the second cylinder, and injecting the fuel into the compressed gases. Thereby the method may be advantageously provided in an engine adapted for a diesel cycle.
According to another aspect of the invention, a method is provided for controlling an internal combustion engine comprising at least one first cylinder and at least one second cylinder with respective reciprocating pistons, first and second intake guides arranged to guide air from a fresh air intake arrangement to the first and second cylinders, respectively, an intake valve arrangement being arranged to control the provision of air to the second cylinder via the second intake guide, a fuel system arranged to inject fuel into the first and second cylinders, a first exhaust guide and a second exhaust guide arranged to guide gases from the first and second cylinders, respectively, towards an exhaust after treatment system, and a recirculation guide extending from the first exhaust guide to the second intake guide, the method comprising
allowing air from the fresh air intake arrangement to be received in the first cylinder,
allowing gases in the form of the air received in the first cylinder or gases including at least a portion of the air received in the first cylinder to be expelled from the first cylinder,
controlling an exhaust valve located in the first exhaust guide so as to reduce or inhibit the transport of gases from the first cylinder to the exhaust after treatment system and to guide to the second cylinder gases expelled from the first cylinder, and
simultaneously controlling the fuel system so as to inject fuel into the second cylinder, so as to provide repetitive, combustions with air in the gases guided to the second cylinder, and controlling the intake valve arrangement for throttling or inhibiting the supply to the second cylinder of air from the fresh air intake arrangement.
Similarly to as mentioned above, receiving in the first cylinder air from the fresh air intake arrangement and guiding to the second cylinder gases expelled from the first cylinder provides for heating by pre-conditioning of the air. Throttling or inhibiting the supply to the second cylinder of air from the fresh air intake arrangement limits temperature reductions caused by introduction of fresh air.
The exhaust valve may be at or downstream of the recirculation guide. The exhaust valve may effectively provide for selectively guiding a portion or all of the gases from the first cylinder into the recirculation guide. Thereby the amount of gases introduced to the first cylinder and reaching an EATS, without passing the second cylinder, may be selectively controlled. Thereby the mass flow through the engine may be effectively controlled.
Preferably the method comprises controlling the exhaust valve comprises controlling the exhaust valve so as to inhibit the transport of gases from the first cylinder to the exhaust after treatment system and to guide to the second cylinder all gases expelled from the first cylinder. By closing the exhaust valve, all gases introduced to the first cylinder may be guided to the second cylinder, and a significant increase of the temperature of gases reaching the EATS at low load operations, cold start events or low ambient temperatures may be provided.
Similarly to as described above, the method may comprise controlling the fuel system so as to inhibit injection of fuel into the air received in the first cylinder. The method may comprise by controlling the fuel system to inject fuel into the first cylinder so as to provide repetitive combustions with the air received in the first cylinder. Thereby, air remaining after first cylinder combustions and combustion products may be thoroughly mixed in the first cylinder and the first exhaust guide, ensuring a homogeneous gas mixture reaching the second cylinder. The amount of fuel injected for each combustion in the first cylinder is preferably smaller than the amount of fuel injected for each combustion in the second cylinder. Nevertheless, the first cylinder may contribute to a crankshaft torque of the engine.
Preferably, the method comprises controlling a ratio of air in the gases expelled from the first cylinder and guided to the second cylinder by controlling the amount of fuel injected into the first cylinder. Thereby, the amount of EGR gases in the second cylinder combustion processes may be controlled to a suitable level, e.g. for limiting NOx production in the second cylinder. The method may advantageously involve not recirculating any exhaust gases to the first cylinder. Thereby, the ratio of air, or the ratio of combustion products, also referred to as an EGR rate, in the gases expelled from the first cylinder and guided to the second cylinder, may be accurately calculated with the need for any sensor in the recirculation guide. This reduces the complexity of the engine, and also eliminates a problem of incorporating a sensor in a potentially harsh exhaust environment in the recirculation guide. Instead the EGR rate may be accurately calculated, e.g. based on the air intake boost temperature, the boost pressure, the volumetric efficiency and the amount of fuel injected into the first cylinder.
Preferably, where the intake valve arrangement comprises an intake divider valve, the second intake guide being arranged to receive air from the fresh air intake arrangement via the first intake guide, controlling the intake valve arrangement comprises at least partly closing the intake divider valve. Thereby the supply to the second cylinder of air from the fresh air intake may be inhibited by closing the intake divider valve. The intake divider valve may be provided e.g. as a flap or a throttle valve. Alternatively first and second throttle valves may be provided in the first and second intake guides, respectively, arranged to block a communication between the fresh air intake and the first and second cylinders, respectively. However, a single intake divider valve may replace two such first and second throttle valves, whereby complexity and cost is reduced.
Advantageously, the method comprises determining the temperature of gases expelled from the second cylinder, wherein the control of the intake valve arrangement is made in dependence on the determined temperature of the gases expelled from the second cylinder. Thereby, an effective way of controlling the temperature of gases reaching an EATS is provided.
Preferably, the method comprises determining a load of the engine, wherein the control of the intake valve arrangement is made in dependence on the determined engine load. Thereby, a further effective way of controlling the temperature of gases reaching an EATS is provided. For example, as the engine load increases, the intake valve arrangement may be controlled so as to gradually increase the amount of air reaching the second cylinder without passing the first cylinder, so as to avoid exhaust temperatures becoming too high.
Preferably, where a recirculation valve is arranged to control the flow through the recirculation guide, the method comprises controlling the exhaust valve and the recirculation valve so as to terminate or reduce the guiding to the second cylinder of gases expelled from the first cylinder, and substantially simultaneously controlling the intake valve arrangement so as to increase the supply to the second cylinder of air from the fresh air intake arrangement. Thereby, a smooth change from the heat mode described above, with gas transport from the first to the second cylinder, to a normal engine mode with all cylinders operating similarly, may take place.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.